Next: The Attributes of a CmpFrame
Up: Compound Frames (CmpFrames)
Previous: Compound Frames (CmpFrames)
A very common use for a CmpFrame within astronomy is to represent a
``spectral cube''. This is a 3-dimensional Frame in which one of the axes
represents position within a spectrum, and the other two axes represent
position on the sky (or some other spatial domain such as the focal plane
of a telescope). As an example, we create such a CmpFrame in which axes
1 and 2 represent Right Ascension and Declination (ICRS), and axis 3
represents wavelength (these are the default coordinate Systems
represented by a SkyFrame and a SpecFrame respectively):
INTEGER SKYFRAME
INTEGER SPECFRAME
INTEGER CMPFRAME
...
SKYFRAME = AST_SKYFRAME( ' ', STATUS )
SPECFRAME = AST_SPECFRAME( ' ', STATUS )
CMPFRAME = AST_CMPFRAME( SKYFRAME, SPECFRAME, ' ', STATUS )
If it was desired to make RA and Dec correspond to axes 1 and 3, with
axis 2 being the spectral axis, then the axes of the CmpFrame created
above would need to be permuted as follows:
INTEGER PERM(3)
...
PERM( 1 ) = 1
PERM( 2 ) = 3
PERM( 3 ) = 2
CALL AST_PERMAXES( CMPFRAME, PERM, STATUS )
Next: The Attributes of a CmpFrame
Up: Compound Frames (CmpFrames)
Previous: Compound Frames (CmpFrames)
AST A Library for Handling World Coordinate Systems in Astronomy
Starlink User Note 210
R.F. Warren-Smith & D.S. Berry
24th May 2011
E-mail:ussc@star.rl.ac.uk
Copyright (C) 2009 Science \& Technology Facilities Council